The recovery of liquid fuels from coal is well documented in the prior art. Various methods for the recovery of liquid fuel from coal have been made, but generally the percentage conversion of coal to liquid fuels have been sufficiently low such that the process is uneconomical. In order to increase the liquid fuel product of coal conversion, attempts have been made to catalyze the coal liquefaction reaction. Various expensive supported catalysts have shown high activity for coal liquefaction catalysis. However, due to the mineral content and coking tendency of coal in liquefaction reactions, the use of such expensive catalysts is unattractive for economic reasons despite catalyst regeneration techniques.
In an attempt to overcome the problem of using expensive supported catalysts in coal liquefaction, the prior art has suggested the use of various inexpensive, potentially throw-away, catalysts which do not require regeneration for economic process operation. Various inexpensive catalysts for coal liquefaction are known, such as iron and its compounds. Alternately, the prior art has suggested the use of low concentrations (ca. 250 ppm of catalyst based on coal) of expensive catalysts in order to render the coal liquefaction reaction economical.
U.S. Pat. No. 2,227,672 discloses the use of a sulfur or phosphate compound of iron, manganese, copper or zinc and a minor proportion of a strong hydrogenation catalyst such as molybdenum, tungsten, cobalt, rhenium, vanadium or nickel or their sulfides as catalysts for the hydrogenation of carbonaceous material such as middle oil, tars and even coal.
U.S. Pat. No. 3,152,063 discloses a process for the hydrogenation of coal without a pasting oil or solvent wherein the coal is subjected to high temperatures after being impregnated with a hydrogenation catalyst such as ammonium molybdate or iron group catalysts and their compounds. The coal is preferably impregnated with catalyst in the form of a solution of a soluble salt or complex. The reaction product is immediately cooled after liquefaction.
U.S. Pat. No. 3,502,564 discloses that hydrogenation catalysts may be formed in situ after the components of the catalyst are impregnated on coal. The catalysts contemplated are the sulfides or naphthanates of nickel, tin, molybdenum, cobalt, iron and vanadium. The process is not utilized in a solvent refining environment.
U.S. Pat. No. 3,619,404 discloses the liquefaction of coal without solvent using supported catalysts such as iron, cobalt, nickel, vanadium, molybdenum or tungsten or compounds of such metals alone or in admixture.
In U.S. Pat. No. 3,745,108 a method for hydrogenating coal to produce a liquid product is set forth wherein at least 25 wt% of the solvent for the liquefaction reaction comprises water. Catalyst for the reaction may be supported on a carrier or impregnated directly on the coal. Catalyst metals include iron, cobalt, nickel, vanadium, molybdenum or tungsten, compounds of these metals and mixtures of the combinations.
Despite the use of various process systems and catalysts and catalyst combinations, the prior art has failed to significantly increase the production of liquid fuels from coal. Therefore, the present invention will be shown to provide a process for increasing the liquid fuel product of a coal liquefaction in a dramatic manner while reducing or maintaining the hydrocarbon gas production and the hydrogen consumption for such a process and thereby providing an economic scheme for the production of liquid fuels from coal. The present invention will be demonstrated to have a higher selectivity for oil than the processes generally known in the prior art, along with a greater coal conversion.